The present invention relates to a digital radio paging receiver and, more particularly, to the signal detecting circuit for such a radio paging receiver to which a plurality of address codewords are assigned.
In a conventional radio paging system, it is usual for any single radio paging receiver to be assigned a single address codeword. One such radio paging system is disclosed in the U.S. Pat. No. 4,194,153 entitled "Digital Radio Paging Communication System" granted to Masaru Masaki et al. Meanwhile, the so-called multi-address paging system, in which a plurality of address codewords are assigned to each radio paging receiver, has been proposed by the British Post Office. References on the latter include "A Standard Code for Radiopaging," published by the British Post Office in July 1979.
If it is attempted to receive with the aforementioned paging receiver of Masaki et al. any selective calling signal by the British Post Office-proposed multi-adddress paging system, the following inconveniences will arise. The capacity of the programmable read-only memory (PROM), which stores the assigned address codewords, and the shift registers, which detect the address codewords, must be increased. This increases circuit complexity and power consumption.
In a situation where the contents of the PROM have to be frequently altered, the PROM will be of the so-called cord plug type, which is mounted on a single-in-line package and plugged into a socket mounted on a printed circuit board (PCB). For a PROM of this cord plug type, an increase in address codewords would entail increases in both socket leads and PCB wires, making the miniaturization of the receiver more difficult.